1. Technical Field
The invention relates to a gasket for ensuring a static seal on the one hand and a dynamic seal on the other. The gasket is intended, in particular, to ensure sealing up-/downstream of a butterfly valve with sealing member operating under conditions of high pressures and/or temperatures. For such uses, metal gaskets are used which ensure a static seal on the body side and a dynamic seal on the sealing member side, or vice versa.
2. Prior Art
The document FR-B1-2 566 870 comprises several types of gaskets designed to ensure sealing between a sealing member and a body. In FIG. 6 thereof, gaskets are proposed which are machined from a single piece, where a dynamic seal is achieved by a chamfered part resting against the sealing member. FIGS. 2 and 4 show gaskets of sheet metal with solid, relatively rigid back pressure rings. The gasket of sheet metal ensures dynamic sealing by means of a metal ring shaped to create contact stresses which are sufficiently great to withstand high pressures. A static seal is achieved by compression of a resilient torus resting on one of the flat parts of the gasket.
Gaskets make use of the concept of self-centering with respect to the sealing member, in such a way as to maintain the sealing stresses when put under pressure and during closure of the sealing member. Radial flexibility of the machined gasket is obtained by a plurality of machined circumferential grooves. The sheet metal gasket comprises a conical connecting zone between the shaped part of the ring and the heel piece.
However, these gaskets are relatively complex and thus expensive to manufacture.
The document DE-C2-26 44 518 describes a one-piece metal gasket. The gasket has a section in the form of a hook, that is to say a heel to ensure a static seal, a bridging piece and a part in the form of an arc of a circle. The bridging piece may be conical or straight in form and is designed to ensure axial flexibility of the gasket, thus permitting it to follow axial displacement of the sealing member, that is to say along the axis of the fluid course.
From DE-OS-24 54 452 elastomer or metal gaskets are known in the form of hooks. In their toroidal portion the gaskets comprise a lip which rests on the shoulder of a housing to limit radial displacement of the gasket.
These gaskets exhibit the disadvantage of not being uniformly compressed if the sealing member is not precisely centered with respect to the dynamic sealing face of the gasket, that is to say where there is radial displacement along the working axis. Since the gasket is not capable of self-centering, sealing about the sealing member is no longer uniform.
The aim of the invention is to find a simple solution to the problem of making a gasket with self-centering capacity.